Computer controlled prosthetic knee device

ABSTRACT

A prosthetic knee provides a single axis of rotation and includes a hydraulic damping cylinder, a microprocessor, and sensors. Based on input from the sensors, the microprocessor selects a flow path within the hydraulic cylinder in order to provide the proper amount of knee resistance to bending for a given situation. The resistance of each flow path within the hydraulic cylinder is manually preset. Changes in gait speed are accommodated by employing a hydraulic damper with intelligently designed position sensitive damping. Moreover, the knee need not be un-weighted to transition from the stance phase to the swing phase of gait. As a result, the knee safely provides a natural, energy efficient gait over a range of terrains and gait speeds and is simpler, less costly, and lighter weight than the prior art.

RELATED APPLICATION

This application claims the benefit of and Paris Convention priority ofU.S. Provisional Application Ser. No. 60/703,588 filed on Jul. 29, 2005,the contents of which are hereby incorporated by reference as if fullydisclosed herein.

BACKGROUND OF THE DISCLOSURE

The present disclosure relates generally to prosthetic devices and, moreparticularly, to prosthetic knees imparted with electronically improvedmotility and safety.

Attempts have been made to overcome the drawbacks associated with thefunction of prosthetic knees by incorporating actuators that areactively, or computer, controlled. Based on inputs from sensors, thecomputer controls the amount of resistance provided by the actuator inorder to adapt to changes in terrain and gait speed and decide when thetransition from stiff to loose, or vice versa, should occur, therebyincreasing safety, improving gait symmetry, and increasing energyefficiency. Current prosthetic knees that incorporate computercontrolled actuators are relatively complex and heavy, which bothincreases cost and is burdensome to the user. Among the attempts toaddress the instant problems are found the following U.S. Pat. Nos.6,764,520 B2, 6,755,870 B1; 6,740,125 B2; 6,719,806 B1; 6,673,117 B1;6,610,101 B2, 6,517,585 B1; 6,423,098 B1; 6,113,642; 5,888,212;5,571,205; and 5,383,939, each of which differs from the instantteachings.

It should, therefore, be appreciated that there exists a continuing needfor a prosthetic knee that provides the gait speed adaptability andsafety of a computer controlled knee but is relatively lightweight andsimple in design. The present disclosure fulfills this need and others.

SUMMARY OF THE DISCLOSURE

A prosthetic knee provides a single axis of rotation and includes ahydraulic damping cylinder, a microprocessor, and sensors. Based oninput from the sensors, the microprocessor selects a flow path withinthe hydraulic cylinder in order to provide the proper amount of kneeresistance to bending for a given situation. The resistance of each flowpath within the hydraulic cylinder is manually preset. Changes in gaitspeed are accommodated by employing a hydraulic damper withintelligently designed position sensitive damping. Moreover, the kneeneed not be un-weighted to transition from the stance phase to the swingphase of gait. As a result, the knee safely provides a natural, energyefficient gait over a range of terrains and gait speeds and is simpler,less costly, and lighter weight than the prior art.

Disclosed is a prosthetic knee system comprising, in combination, aframe, a computer, a rotor connected to the frame providing at least oneaxis of rotation about the prosthetic knee and using a hydraulic dampingcylinder that compresses or extends to facilitate resistance torotation, the hydraulic damping cylinder further comprising: aprosthetic knee flexion resistance path and a prosthetic knee extensionresistance path; wherein at least one of the flexion resistance path andthe extension resistance path further comprises a plurality of flowresistance paths; and wherein the computer determines the resistance ofthe flow resistance path.

Similarly disclosed is a prosthetic knee system, comprising, incombination a frame, a computer, a rotor connected to the frameproviding at least one axis of rotation about the prosthetic knee andusing a hydraulic damping cylinder to facilitate resistance to rotation,the hydraulic damping cylinder further comprising: a low force flexionresistance flow path; a high force flexion resistance flow path; and anextension resistance flow path, wherein the high force flexionresistance flow path is the knee's default and the computer determineswhen to use the low force flexion resistance flow path.

Still further disclosed is a improved prosthetic knee device comprisinga computer and a plurality of parallel flow paths of varying flowresistance.

In yet another aspect of the present disclosure, a method of mimicking ahuman gait with a computer and sensor disposed in a prosthetic knee isdisclosed comprising, in combination, providing a prosthetic knee withvariable damping, wherein the variable damping comprising at least:waiting for a maximum force to be registered in a heel sensor; waitingfor a maximum force to be registered in a toe sensor; and initiating asecond trigger.

Finally disclosed is a prosthetic knee comprising a frame and a rotorconnected to the frame providing at least one axis of rotation about theprosthetic knee and using a hydraulic damping cylinder with positionsensitive damping to facilitate resistance.

DRAWINGS

Embodiments of the present disclosure will now be described, by way ofexample only, with reference to the following drawings in which:

FIG. 1 is a graph of an exemplary walking gait cycle on level ground foran observed leg, in which knee position is provided along the y-axis andpercentage of gait cycle is provided along the x-axis.

FIG. 2 is a back perspective view of a prosthetic knee in accordancewith the disclosure.

FIG. 3 is a front perspective view of the prosthetic knee of FIG. 2.

FIG. 4 is a front elevational view of the prosthetic knee of FIG. 2.

FIG. 5 is a right-side elevational view of the prosthetic knee of FIG.2.

FIG. 6 is a back elevational view of the prosthetic knee of FIG. 2.

FIG. 7 is a simplified schematic describing an exemplary operation ofthe hydraulic cylinder of FIG. 9A.

FIG. 8 is a simplified block diagram describing an exemplary operationof the software to control the solenoid-actuated spool valve of thehydraulic cylinder of FIG. 9A.

FIG. 9A is a back elevational view of the hydraulic cylinder of theprosthetic knee of FIG. 2.

FIG. 9B is a cross-sectional view of the hydraulic cylinder of FIG. 9A.

FIG. 10 is a close-up, back elevational view of the hydraulic cylinderof FIG. 9A, depicting the solenoid and high force compression, or stanceflexion, resistance adjustor (needle valve).

FIG. 11 is a cross-sectional view of the spool valve and solenoid of thehydraulic cylinder of FIG. 9A.

FIG. 12 is a cross-sectional view of the high force compression, orstance flexion, resistance adjustor of the hydraulic cylinder of FIG.9A.

FIG. 13 is a cross-sectional view of the latching mechanism of thehydraulic cylinder of FIG. 9A.

DETAILED DESCRIPTION

Makers of prosthetic knees have long attempted to mimic a naturalwalking gait. For purpose of illustration, this may be understood to bea reference to an exemplary walking gait cycle (level ground) as isgraphically presented in FIG. 1. The chart depicts the knee position,along the y-axis, for an observed leg with respect to a percentage ofgait cycle, along the x-axis. In the graph, the gait cycle initiates asthe heel of the observed leg strikes the ground.

For each leg, a walking gait can be divided into two phases, a stancephase and a swing phase. The stance phase is defined as the period oftime during which the foot of the observed leg is weighted. The swingphase is defined as the period of time when the foot of the observed legis un-weighted. As a point of reference, the transition (T) from thestance phase to swing phase occurs at about 40 percent of the gaitcycle.

The stance phase of a walking gait begins as the heel strikes theground, indicated by point (I) on the graph. Upon heel strike, the kneeflexes slightly to absorb some of the impact forces acting on the limbdue to weight acceptance—referred to as “stance flexion” of the knee.

After the foot is flat on the ground, the shin begins to rotate forwardabout the ankle. As the shin rotates, the knee remains flexed in orderto minimize the rise of the person's center of mass as it passes overthe ankle joint center. As the shin continues to rotate forward and thecenter of mass progresses forward, the weight acting on the limb movestowards the toe of the foot. The force of the weight acting on the toegenerates a torque about the knee joint that tends to straighten, orextend, the knee—referred to as “stance extension” of the knee. Stanceextension continues until the transition point to the swing phase.

Soon after the knee is completely extended, the toe pushes off theground, stance ends, and swing begins. As the toe pushes off the ground,the knee rapidly flexes to about 60 degrees—referred to as “swingflexion” of the knee. In order to keep the toe from stubbing on theground, the knee will remain flexed as the leg rotates, or swings,forward about the hip joint. As the leg continues to swing forward theknee will extend until it is nearly straight—referred to as “swingextension” of the knee. Soon after the knee is fully extended, the heelof the foot will strike the ground again, and the gait cycle begins allover.

During the level-ground walking gait cycle described above, the knee,together with the muscles acting on it, functions primarily as anabsorber of energy. In attempts of achieving a natural walking gait, ithas been known to incorporate hydraulic dampers in prosthetic knees tocontrol the motion of the knee joint during both the stance and swingphases of the gait cycle. In such prosthetic knees, during the stancephase, the hydraulic damper provides a relatively high amount ofresistance to motion, or damping, making the knee joint comparativelystiff and able to support high forces. During the swing phase, thehydraulic damper provides a relatively low amount of resistance makingthe knee joint comparatively loose and able to swing freely. Thus,generally speaking, such prosthetic knees have both a stiffconfiguration and a loose configuration. To achieve a natural, energyefficient gait the hydraulic damper must provide the proper amount ofresistance in each of these configurations, and the transition betweenthese configurations must occur quickly and at the proper time in thegait cycle. In addition, to insure safety the transition should neveroccur when the user is not walking and the prosthetic limb is weighted.

In current prosthetic knees that use passive mechanical hydraulicdampers, the amount of resistance provided by the damper is controlledin both the stiff and the loose configurations by metering the flow ofhydraulic fluid through valves that are manually set. The transitionbetween the stiff and loose configurations is triggered by theoccurrence of mechanical events (e.g., full extension of the hydrauliccylinder and reversal of hydraulic flow). There are two major drawbacksof knees designed this way: (1) the amount of resistance provided by thehydraulic damper is optimal for only a single gait speed and; (2) themechanical events that trigger the transition from stiff to loose, orvice versa, can occur at the wrong time and thereby introduce a safetyhazard.

The present disclosure presents a novel way to actively and dynamicallycontrol hydraulic dampers in prosthetic knees. According to embodimentsof the present disclosure, a computer selects various flow paths. Thevarious flow paths provide varying degrees of resistance to a flowfluid. Controlling the flow path allows the computer to selectivelydampen a hydraulic damping cylinder and consequently vary the resistanceof the prosthetic knee depending on the phase of the gait cycle.

Referring now to an embodiment shown in FIG. 2, there is shownprosthetic knee 10 having hydraulic damping cylinder 12 disposed inframe 14. In the exemplary embodiment, hydraulic damping cylinder 12 maybe any damping cylinder that would be well known to a person of ordinaryskill in the art. As depicted in FIG. 11, the hydraulic damping cylindercontains normally-closed, solenoid-actuated spool valve 52. The state ofspool valve 52 is controlled via a processing system having a digitalprocessor, or computer (not shown), mounted on a printed circuit board(PCB) 18, which communicates with sensors disposed about the knee. Poweris provided by battery pack 19 mounted on frame 14 or in anothersuitable location. As discussed below, using input from the sensors theprocessing system controls via spool valve 52, the transition from whenthe knee joint is stiff to when it is loose ensuring safe operation ofthe knee.

Referring again to FIG. 2, prosthetic knee 10 includes rotor 20 mountedto frame 14, defining a knee joint center about which the knee bends.Rotor 20 is attached to a proximal end of frame 14 such that proximalmount 22 can be attached to rotor 20. Proximal mount 22 is configured tomate with a limb socket (not shown) that is conformed to the user'sremnant limb.

Hydraulic damping cylinder 12 is attached at its proximal end to rotor20 and at its distal end to frame 14, allowing hydraulic dampingcylinder 12 to regulate knee movement. Thus, according to an embodimentof the instant teachings, when the knee angle is increasing, hydraulicdamping cylinder 12 is being compressed, and when the knee angle isdecreasing, hydraulic damping cylinder 12 is being extended.

Sensors located throughout frame 14 detect and convey data to thecomputer. Extension sensor 28 is spaced about the knee to sense therelative position of the knee joint. In the exemplary embodiment,extension sensor 28 is disposed about the proximal end of the knee andincludes a magnetic reed switch attached to the PCB 18 and a magnetattached to rotor 20 in spaced relationship to the magnetic reed switch.When the knee is fully extended, i.e., knee angle of about zero degrees,the magnetic reed switch is disposed near the magnet. As the knee isbent, the reed switch and the magnet rotate away from each other. Inputfrom the magnetic reed switch is provided to the computer system. As aresult, the computer can determine when the knee is fully extended.

Likewise, front load sensor 30 and rear load sensor 32, are disposed ina distal end of prosthetic knee 10 between frame 14 and distal mount 38,to which attaches a lower leg prosthesis (not shown). These load sensorsdetermine how much load is being applied and the distribution of theload on the foot throughout the gait cycle. For example, as the heelstrikes the ground at the beginning of the gait cycle, rear load sensor32 will detect a compressive load and front load sensor 30 will detect atensile load. Then, as the weight shifts from heel to toe during thestance phase of the gait cycle, the load detected by rear load sensor 32will become a tensile load while the load detected by front load sensor30 will become a compressive load. As a result, the computer candetermine when the transition from the stance phase to the swing phaseof the gait cycle should occur and actuate spool valve 52 of thehydraulic damping cylinder 12 at the proper time, as described below.

FIG. 7 depicts a simplified schematic of the hydraulic circuit withinhydraulic damping cylinder 12. Hydraulic damping cylinder 12 includespiston 40 mounted for axial movement within main fluid chamber 42 and afluid, which may be any hydraulic fluid, such as bicycle or motorcycleshock fluid, known to a person of ordinary skill of the art.Progressive-type hydraulic cylinders, including Mauch-type cylinders,may be used in which the cylinder damping changes as the angle of theknee joint changes. The choice of cylinder will be readily apparent to aperson of ordinary skill in the art depending on the desiredcharacteristics of the hydraulic cylinder.

As the piston moves in the direction of compression, fluid flows throughtwo paths. Some fluid flows out of main chamber 42 into fluid reservoir54 through first needle valve 50, which provides high force compression,or stance flexion, resistance (R_(HC)). The rest of the fluid flowsacross the piston through a pressure sensitive control valve 34 thatprovides the low force compression, or swing flexion, resistance R_(LC).In embodiment, pressure sensitive valve 34 is a progressive dampingvalve as disclosed in U.S. Pat. Nos. 5,190,126 and 6,978,872, both ofwhich are incorporated by reference as if fully disclosed herein.Progressive damping allows prosthetic knee 10 to mimic a more naturalswing during swing flexion.

In a normal human gait, swing flexion is arrested at approximately 60degrees from a straight leg. During the initial swing flexion phasethrough about 30 degrees, the leg swings freely. However, from about 30degrees to about 60 degrees the brain decelerates the swing until it isarrested at about 60 degree. According to an embodiment of the presentdisclosure, there is utilized a progressive damping system to mimic thenatural effect in prosthetic knees. The progressive damping systemcomprises specialized pressure sensitive control valve 34 (R_(LC))disclosed in the above referenced patents. Pressure sensitive controlvalve 34 allows mostly free swing between about 0 degrees and about 30degrees and thereafter progressively dampens movement by increasingresistance until arrest of swing flexion at about 60 degrees.

Normally-closed, solenoid-actuated spool valve 52 is parallel to firstneedle valve 50. Therefore, when spool valve 52 is opened, flow bypassesfirst needle valve 50, essentially eliminating the high forcecompression resistance. As piston 40 moves in the direction ofextension, fluid again flows through two paths. Some fluid flows fromfluid reservoir 54 back into main fluid chamber 42 via check valve 51with very little resistance. The rest of the fluid flows across piston40 through second needle valve with shim stack 41, which providesextension, or swing extension, resistance (R_(E)).

Both the high force compression resistance (R_(HC)) and the extensionresistance (R_(E)) may be adjusted by the user by manually changing theposition of first needle valve 50 and second needle valve with shimstack 41, respectively. Gas chamber 56 is filled with a gas, typicallyair, and disposed adjacent to fluid reservoir 54, separated by flexiblebladder 58. The low force compression resistance (R_(LC)) is regulatedby the user by changing the pressure in the gas chamber, in embodiments.In other embodiments, an independent floating piston may replace gaschamber 56 and bladder 58 to accomplish the same purpose and would beunderstood by a person of ordinary skill in the art.

Spool valve 52 is actuated by solenoid 60. When solenoid 60 isde-energized, return spring 66 holds spool valve 52 in a closedposition. Energizing solenoid 60 causes the spool to move in thedirection opposite to the force of return spring 66, thereby openingspool valve 52. When spool valve 52 achieves an open position, latchingmechanism 62, shown in FIG. 13, prevents return spring 66 from closingspool valve 52. In an embodiment, latching mechanism 62 includescantilever beam 64. However, other approaches may be used, as would beknown to a person of ordinary skill in the art. When hydraulic flowreverses, latching mechanism 62 releases spool valve 52 and returnspring 66 moves the spool to the closed position, thereby closing spoolvalve 52.

Operation of hydraulic damping cylinder 12 during a normal walking gaitcycle works in conjunction with the operation of the valves. As heelstrike occurs, the ground reaction forces may tend to bend prostheticknee 10 and compress hydraulic damping cylinder 12. At this moment,solenoid 60 is de-energized thus spool valve 52 is closed and the fluidflows through both the first needle valve 50 and the low forceresistance channel (R_(HC) and R_(LC)). Therefore, hydraulic dampingcylinder 12 provides a high amount of damping causing the knee joint tobe relatively stiff and able to support the user's weight. As the user'sweight begins to come off the foot at the end of the stance phase thecomputer energizes solenoid 60 to open spool valve 52, which bypassesthe high force resistance of first needle valve 50. Once latchingmechanism 62 engages and is holding spool valve 52 open, solenoid 60 isde-energized to conserve energy. According to embodiments, thetransition between high resistance compression and low resistancecompression occurs in 10 ms or less. With spool valve 52 open, thedamping decreases allowing prosthetic knee 10 to bend rapidly duringswing flexion. As the lower leg swings forward and swing extensionbegins, the direction of hydraulic flow within the cylinder is reversed,and latching mechanism 62 releases the spool. Return spring 66 thencloses spool valve 52, which causes hydraulic damping cylinder 12 toonce again be able to provide a high amount of damping when the heelstrikes the ground at the start of the next gait cycle.

With reference now to FIG. 8, a computer system controls the damping ofprosthetic knee 10. According to an embodiment, the computer is aninterrupt driven state machine that runs a control algorithm. Theinterrupt cycle time is 1 ms, or 1000 Hz. The computer allows only asingle state change per cycle. Generally, the main function and outputof the computer is to switch the knee between a stiff configuration anda freely swinging configuration, which is accomplished by the computercontrol of solenoid 60. Sensors disposed in frame 14 of prosthetic knee10 provide the computer with the input required to energize solenoid 60at the proper time during the gait cycle.

According to an embodiment, extension sensor 28 is digital. Thus, ateach interrupt, the computer reads the state of extension sensor 28.Conversely, both front load sensor 30 and rear load sensor 32 are analogsensors. Consequently, the computer uses a two interrupt sequence toobtain a digital signal from the analog load sensors. At the firstinterrupt, an analog to digital conversion algorithm is initiated usingdata from each load sensor. At the second interrupt, the computerretrieves the digital data output from the analog to digital conversionalgorithm. Once the computer has digital readings from the load sensors,the computer calculates a load calculation and difference of a momentcalculation.

The load calculation tells the computer whether the foot, shin, and kneeare loaded. In an embodiment, the load is calculated by adding theoutput of front load sensor 30 and rear load sensor 32. The momentcalculation takes the difference between front load sensor 30 and rearload sensor 32. When the heel is predominantly weighted, the momentcalculation is negative. However, when the toe is predominantlyweighted, the moment calculation is positive. The computer uses the loadcalculation and the moment calculation to determine the amount ofdamping to apply to the knee. Specifically, the state machine uses datafrom the sensors in conjunction with a timer algorithm to advancethrough progressive phases of a control algorithm.

The control algorithm controls solenoid 60, which actuates spool valve52. Each cycle begins just before heel strike at phase 1 of FIG. 8 andends at phase 7 when the computer causes solenoid 60 to be energized. Ashort time before the heel of the foot strikes the ground, the kneebecomes fully extended. Extension sensor 28 detects the straightened legand communicates a signal to the computer. According to an embodiment,the sensor detects a straightened leg when the knee is within 5 degreesof full extension. Phase 1 is the default start state in the exemplaryembodiment.

Once an extend signal is detected from extension sensor 28, thealgorithm advances to phase 2. During phase 2, the computer allows a setperiod of time to elapse. The period of time is customizable byindividual users, although the default timing will be appropriate formost users. The processing system will not proceed to phase 3 until theset time period elapses, after which the algorithm will automaticallyadvance to phase 3.

Certain conditions, however, will cause phase 2 to either reset theperiod of time that must elapse before phase 3 or return the algorithmto phase 1. According to embodiments, the algorithm will return to phase1 or 2 if the load drops below a set minimum value or the extensionsensor 28 is sensed in an open position. Whether the algorithm returnsto phase 1 or phase 2 is inconsequential and is a matter of preferencefor the implementer of the algorithm because extension sensor 28 isclosed, which will, upon returning to phase 1, trigger the algorithm toautomatically advance to phase 2. Thus, the only difference betweenwhether the algorithm returns to phase 1 or resets phase 2 is thatreturning the algorithm to phase 1 will cause a delay of one cycle, or 1ms, before phase 1 advances to phase 2.

During phase 3 the computer monitors the load reading from front loadsensor 30 and rear load sensor 32 and waits for a “heel moment.” Duringphase 3 the algorithm waits until the load is predominantly on the heel.According to an embodiment, a “heel moment” occurs when the momentcalculation is at a minimum. Once a “heel moment” event occurs, thealgorithm then advances to phase 4. If, during phase 3, the load dropsbelow a set minimum value or the extension sensor 28 is sensed in anopen position, then the algorithm will return to either phase 1 or phase2, as previously described.

During phase 4 the load is in the process of transferring from the heelto the toe. The computer monitors the moment calculation. Once itexceeds a set value, for example ⅔ of the max moment calculation (i.e.,a given load is shifted from heel to toe), the algorithm advances tophase 5. The computer times phase 4. If the moment calculation fails toexceed the set value before a set time elapses, then the algorithmreturns to phase 3. If, during phase 4, the load drops below a setminimum value or the extension sensor 28 is sensed in an open positionat the start of phase 4, the algorithm returns to phase 1 or phase 2, aspreviously described. In embodiments, the moment calculation value thatmust be exceeded to advance to phase 5 is adjustable on a per userbasis.

If, during phase 4, the extension sensor 28 opens before the value ofthe moment calculation exceeds the set value, then phase 4 proceeds witha modified set of values for the remainder of the cycle optimized fordescending type movement, such as moving down inclined surfaces.According to embodiments, these values may be adjusted on a per userbasis. By adjusting the values for descending type movement, the kneewill be able to swing to prevent toe stubbing, improving safety.Generally, the value of the moment calculation that must be exceeded toproceed to phase 5 for descending type movement will be set lower thanthe normal, level ground value because the load will be more focused onthe heel than the toe in these types of situations.

During phase 5 the algorithm waits until the moment calculation reachesa maximum. The algorithm then proceeds to phase 6 once it detects thatthe moment calculation drops below the measured maximum. Variouscriteria may be used, according to embodiments, to determine when toadvance to phase 6, for example, including when the moment calculationdrops below a preset percentage of the maximum, when the momentcalculation minus a preset value is lower than the maximum, or when themoment calculation is less than a preset trigger point. In the lattercase, the algorithm may advance directly to phase 7, in embodiments.

During phase 6, the algorithm monitors the moment calculation. Once itdrops below a preset trigger point, the algorithm advances to phase 7and energizes solenoid 60 for swing flexion and extension. Aftertriggering solenoid 60, the algorithm advances to phase 1 and awaits theclosing of extension sensor 28, which starts the control cycle over. Thepreset trigger point is adjustable on a per user basis and may havevariable values for normal movement and descending type movements.

According to embodiments, users may personalize the timing settings ofthe timed phases. Control of the computer settings may be accomplishedby use of a Bluetooth signaling mechanism, for example. According toexemplary embodiments, the computer on the knee integrates a Bluetoothreceiver that receives signals from a computer device containing aBluetooth transceiver. Examples of suitable computer may be a home PC ora PDA. Software compiled specifically for the computer platform, forexample a PDA, allows a user to monitor and adjust settings for thetimings of the applicable phases. Setting data may be stored in flashmemory or an equivalent electronic storage media within prosthetic knee10. Adjustment of the trigger points and other user configurablevariables may be similarly accomplished.

The present disclosure has been described above in terms of presentlypreferred embodiments so that an understanding of the present disclosurecan be conveyed. However, there are other embodiments not specificallydescribed herein for which the present disclosure is applicable.Therefore, the present disclosure should not to be seen as limited tothe forms shown, which is to be considered illustrative rather thanrestrictive.

1. A device, comprising, in combination: a prosthetic knee comprising: aframe; a computer; a hydraulic damping cylinder; and a rotor connectedto the frame; wherein the rotor provides at least one axis of rotationabout the prosthetic knee and wherein the hydraulic damping cylinderfacilitates resistance to rotation, the hydraulic damping cylinderfurther comprising: a low force flexion resistance flow path; a highforce flexion resistance flow path; and an extension resistance flowpath, wherein the high force flexion resistance flow path is the knee'sdefault flow path and the computer determines when to use the low forceflexion resistance flow path.
 2. The device of claim 1, wherein in thelow force flexion resistance flow path a hydraulic fluid exits a maincylinder chamber and passes through a spool valve into a reservoirhaving a compressible gas chamber disposed adjacent thereto.
 3. Thedevice of claim 2, wherein activating a solenoid allows hydraulic fluidto bypass the high force flexion resistance flow path by effecting theopening of the spool valve for the duration of the low force cycle. 4.The device of claim 3, wherein once the spool valve opens, a latchingmechanism is triggered, the latching mechanism holding the spool valveopened after the solenoid is deactivated.
 5. The device of claim 4,wherein upon a reversal of the hydraulic fluid flow, the latchingmechanism releases the spool valve causing the spool valve to close, anda needle valve allows hydraulic fluid to flow through an extensionpiston bypass resistance flow path into the main fluid chamber, wherebyresistance in the extension resistance flow path can be manuallyadjusted with the needle valve.
 6. The device of claim 5, wherein oncethe spool valve is released, a return spring causes the spool valve toclose.
 7. The device of claim 5, further comprising one or more checkvalves that inhibit back flow through the hydraulic fluid flow paths. 8.The device of claim 1, further comprising at least one sensor, whereinthe at least one sensor provides useful data to the computer.
 9. Thedevice of claim 8, wherein the sensors comprise at least: an extensionsensor, the extension sensor providing useful data to the computerregarding the relative position of the prosthetic knee joint; a frontload sensor, the front load sensor providing useful data to the computerregarding load on a foot; and a rear load sensor, the rear load sensorproviding useful data to the computer regarding load on the foot. 10.The device of claim 8, wherein the computer regulates damping within thehydraulic damping cylinder, the computer receiving data from the sensorsand in response causing triggering the high force flexion resistanceflow path or the low force flexion resistance flow path during flexionof the prosthetic knee.
 11. The device of claim 2, wherein a reservoiris separated by a physical bladder forming an adjustable fluid chamberand an adjustable compressible gas chamber, and wherein resistance ofthe low force flexion resistance flow path is regulated influenced by agas pressure of a gas in the adjustable compressible gas chamber. 12.The device of claim 2, wherein resistance of the low force flexionresistance flow path is regulated in part by manual adjustment of anadjustable needle valve in a low force compression piston bypassresistance flow path.
 13. The device of claim 1, wherein the hydraulicdamping cylinder is a hydraulic damping cylinder with position sensitivedamping.
 14. The device of claim 13, wherein the hydraulic dampingcylinder minimizes damping during a swing flexion phase of knee movementfrom about 0 to about 30 degrees and progressively increases dampingfrom about 30 degrees to about 60 degrees, wherein resistance stopsflexion of the prosthetic knee at about 60 degrees.